1. Field of the Invention
The present invention relates to an improved process for producing octa-2,7-dien-1-ol by reacting butadiene with water.
2. Description of the Prior Art
Synthesis of octa-2,7-dien-1-ol by reacting butadiene with water in the presence of a palladium catalyst is known. Since, as is well known, palladium catalysts are very expensive noble metal catalysts, it is important for the purpose of commercially producing octa-2,7-dien-1-ol at a low cost and on a large scale, to solve the following technical problems 1) through 4).
1) to achieve a high reaction rate at a commercially permissible palladium catalyst concentration (several milligram atoms as palladium atom per 1 liter of reaction mixture);
2) to assure a sufficiently high selectively to octa-2,7-dien-1-ol;
3) to allow the activity of the palladium catalyst to be maintained stably over a long period of time; and
4) to assure that the product octa-2,7-dien-1-ol can be efficiently separated from the reaction mixture without entailing a deactivation of the palladium catalyst.
While octa-2,7-dien-1-ol is generally separated by distilling the reaction mixture containing the palladium catalyst, a detailed study by the present inventors revealed that when the distillation temperature exceeds about 120.degree. C., the palladium catalyst tends to be decomposed to the metal and inactivated.
As a process that would solve the above technical problems, two inventors including one of the present inventors have already proposed the following production process (see U.S. Pat. Nos. 4,356,333 and No. 4,417,079), which comprises:
(I) reacting butadiene with water in an aqueous sulfolane solution containing a carbonate and/or bicarbonate of a monodentate tertiary amine having a basicity constant (pKa) of at least 7 in the presence of a palladium compound and a hydrophilic monodentate phosphine in an amount of at least 6 moles per 1 gram atom of the palladium, to synthesize octa-2,7-dien-1-ol,
(II) separating the product octa-2,7-dien-1-ol by extracting at least part of the reaction mixture obtained in step (I) with a saturated aliphatic hydrocarbon, a mono-olefinic hydrocarbon or an alicyclic hydrocarbon, and
(III) recycling at least part of the extraction residue containing the catalyst components as obtained in step (II) to step (I).
According to the process described in U.S. Pat. Nos. 4,356,333 and 4,417,079, octa-2,7-dien-1-ol can be produced at high reaction rate and selectivity even when a palladium catalyst is present in a low concentration and, in addition, can be separated from the reaction mixture without entailing a deactivation of the palladium catalyst, thus permitting re-use of the palladium catalyst by recycling. However, it has been found that even with this process there still remains, when a long-term continuous operation is conducted on commercial scale, the following problems to be solved. There are eluted, although in extremely small amounts, catalyst components such as palladium, phosphorus compound, tertiary amine and sulfolane, into the extract obtained upon separation of octa-2,7-dien-1-ol from the reaction mixture. When this extract is subjected to distillation as it is to separate unreacted butadiene, the extracting solvent used and catalyst components from octa-2,7-dien-1-ol, most of the eluted palladium catalyst precipitates as metal in the waste, whereby the reboiler used decreases its thermal efficiency with time to render the separation by distillation difficult to continue and the amount of by-produced high boiling substances increases. U.S. Pat. No. 4,356,333 also describes that trace amounts of catalyst and phosphine contained in the extract can be removed by washing the extract with for example an aqueous sulfolane solution prior to separation treatment of octa-2,7-dien-1-ol from the extract. According to the study made by the present inventors, however, the recovery rate of palladium catalyst from the extract in this process is 30 to 40% at most, and it is difficult, by simply improving the apparatus used to achieve high washing efficiency, to recover the palladium catalyst from the extract to such an extent as to suppress the decrease in thermal efficiency of reboiler and generation of high boiling by-products. Furthermore, the palladium compound and phosphorus compound recovered by this distillation have changed to forms that no longer have catalyst activity as they are and, hence, require to be retreated in some manner. A process requiring such retreatment cannot be said to be economical. It is needless to say that, where such compounds as n-octanol are produced at a comparatively low price and commercially in large amount, serious problems will arise from even a few percentages of: a) increase in elution of palladium catalyst into the extract, b) decrease in recovery rate of the catalyst component, c) increase in by-production of high-boiling compounds, d) decrease in the thermal efficiency of reboiler, and the like.
Accordingly, a principal object of the present invention is to provide a process for producing octa-2,7-dien-1-ol that is free from the above problems.
This object as well as other objects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description.